Blood gas measuring apparatuses are known which are designed for measuring, by means of suitable measuring electrodes, blood pH, concentration of dissolved carbon dioxide in blood, expressed as P.sub.CO.sbsb.2 (the partial pressure of carbon dioxide) and the concentration of dissolved oxygen in the blood, expressed as P.sub.O.sbsb.2 (the partial pressure of oxygen), and one known fully automatic blood gas measuring apparatus (Radiometer ABL1, described, e.g. in U.S. Pat. No. 3,874,850) also simultaneously measures the blood hemoglobin content (Hb) which is otherwise normally measured separately.
From these four central parameters may be calculated various derived parameters which are of great significance to the judgement of so-called acid-base status of the organism.
The measurements referred to above are all relative measurements where the unknown sample is compared with standards. Hence, the quality of these standards is decisive to the quality of the measurement of the single parameters.
When using manual or semiautomatic blood gas measuring equipment, great technical skill is nowadays a requirement to the user of the measuring equipment in order to obtain measurements of satisfactory quality. The technical level of the user may be lower when a fully automatic self-calibrating equipment is used, e.g. of the type described in the above-mentioned U.S. Pat. No. 3,874,850, but this does not remove the necessity or desirability of being able to check the measuring quality of the equipment, including the quality of the standards, calibration liquids, etc., of the equipment, using a known reference.
Even though it is, in principle, generally known to check a measuring equipment by introducing a sample of known properties into the equipment, this is a great problem in connection with equipment for measuring pH - P.sub.CO.sbsb.2 - P.sub.O.sbsb.2 - and optionally Hb.
A sample (a blood sample or another aqueous solution) of this type is normally not stable during any longer period (CO.sub.2 and O.sub.2 escape from the sample) which means that the sample must be prepared on the spot by the user. Normally, this gives rise to problems involving extraordinarily much labor, expensive extra equipment and uncertainty, as the preparation process is technically rather complicated.
All over the world, there is in our days an interest in a control system for measuring values from equipment of the type mentioned, as this equipment is used directly in connection with patient treatment and often under extremely critical circumstances (e.g. during surgery).
In the U.S.A., Congress has dealt with this problem during recent years, and at present, the legislation tends toward requiring that the "supplier of blood data", e.g. the head doctor of the laboratory, shall be able to prove, at any time, that the measuring equipment used is able to yield reliable data in that it has been checked by means of a system independent of the normal calibration system of the equipment (quality control).
Hence, the general desire to-day (also outside the U.S.A.) is that one would be able to buy for this quality control, small containers with samples of known composition and of great reliability.
All blood gas measuring equipment commercially available requires frequent calibration, usually with intervals of some hours. For this purpose, the known art uses, for certain types of equipment, various calibration liquids, some of which (e.g. pH buffer mixtures) are commercially available in small containers and show high reliability with respect to keeping the stated pH values, whereas the calibration liquids for the calibration of other parts of the measuring equipment, e.g. the P.sub.CO.sbsb.2 measuring equipment and the P.sub.O.sbsb.2 measuring equipment, are at the moment not commercially available in easily handled packages. Some technically advanced blood gas analyzers, e.g. the above-mentioned fully automatic Radiometer ABL1 gas measuring equipment, use solutions which in the equipment proper are equilibrated with known gas mixtures to obtain well-defined values for pH, P.sub.CO.sbsb.2, and P.sub.O.sbsb.2, and the calibration liquids thus prepared in the equipment and showing well-defined data are used for the calibration within the equipment, without being transferred to separate containers.
It would be of great interest to be able to perform the very calibration of the blood gas measuring equipment, especially semiautomatic equipment, using a handy reference liquid which may be produced and packed in suitable unit portions and distributed and stored with retention of its relevant data with high exactitude and reliability, in order that the calibration of the blood gas measuring equipment can be performed simply by introducing a unit portion or a part thereof in the equipment without the necessity of any special preparation or checking of the liquid.